If horsepower is your main concern, the long tube intakes will always yield better horsepower gains than the short ram intakes. Regardless of what the K&N Typhoon ads claim. I've seen dyno results putting the Typhoon short ram gain around +6 or +7 at 7,000 rpm. If you can, spend a little more to go with the long tube intake - either the Injen or the Stillen Gen 3. That's where you'll see double-digit HP gains.
And that's coming from a guy with the K&N Typhoon. I like it, but would've gone with a long tube intake if I could have.
As far as voiding the warranty, I couldn't tell you. I'm hoping to find out, myself.